A cellular radio network may comprise cells of various sizes. In sparsely populated areas, the cells are often large macro cells, whereas in population centres, it is possible to use small cells, i.e., micro or pico cells. The diameter of a pico cell is typically at most a few dozen metres, and the transmission power level used in it is at most a few hundred milliwatts, the diameter of a micro cell is at most a few hundred metres, and the transmission power level at most a few watts, and the diameter of a macro cell is at most a few dozen kilometres, and the transmission power level at most a few dozen watts. Macro cells are typically used to cover large areas, a micro cell covers a multi-storey office building and its vicinity, for instance. One or more pico cells are generally used in a cellular radio system intended for indoor environments, and a pico cell covers a few office rooms, for instance. The size hierarchy of cells can also have several levels, and the definitions of the names may vary. Cells of various sizes can be placed on top of each other, if necessary.
A prior art cellular radio system intended for indoor environments utilises known radio system technology and a data network. The radio system can be a CDMA or a GSM radio system whose terminals and base stations are integrated together by means of computer technology using a data network for data transmission. The data network, i.e. telecommunications network, can be an IP (Internet protocol) network, for instance, which connects base station controllers and a system controller. The operation of a base station controller can be distributed to an IMC (intranet mobile cluster) and an MS-IP controller, the IMC being able to manage a few base stations and the MS-IP controller being able to manage dozens of base stations. The MS-IP controller takes care of the signalling between the base station controller and the IP network. The base stations, base station controllers and the system controller are connected to each other through the data network whose data transmission rate depends on the load. The base stations are connected over radio path to terminals in their coverage area, and also generally transmit general signals, such as a BCCH (broadcast control channel) signal of a BCCH in an indoor radio system based on the GSM radio system.
Data transmission rate variations caused by data network load in particular can considerably decrease the quality of a signal or cut off the connection completely. A partial or complete failure of base station transmitters can also easily remain undetected in prior art solutions and cause great problems to users in that the signal disappears or its quality decreases.